<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>
    <script>
        var a = parseInt(prompt("请输入一个数字"));
        //累加器，初始值一定是0
        var xyh = 0;
        //从1加到那个数字
        for (var n = 2; n <= a; n++) {
            xyh += (n + 1) / n;
        }
        //输出最后的结果
        console.log(xyh);
    </script>
</body>
        
</html>